Study on the performance and strain aging behavior of solid-solution state low-carbon steel

Abstract

Herein, the strain aging behavior of low-carbon steel subjected to heating at 850 °C followed by a 5-min holding time and water cooling cycle was studied. Various aging periods were tested using a 2% pre-deformation and baking step at 170 °C. The aging performance was characterized by tensile testing. Furthermore, the organizational structure variation was analyzed with transmission electron microscopy (TEM) and by measuring the internal friction of the low-carbon steel. Finally, age hardening mechanisms were discussed. The test results indicated that when the aging period ranged between 5 and 100 min, both the yield strength and tensile strength declined rapidly and the bake-hardening (BH) value decreased from 104.6 MPa to −13.2 MPa. In addition, morphological differences were observed: fine carbides gradually formed in the microstructure and continued to coarsen over time. Furthermore, the height of the Snoek peak decreased rapidly and was accompanied by the appearance of 3 internal friction peaks, denoted P1, P2 and P3. When the aging period exceeded 100 min, the yield strength, tensile strength and BH value varied only slightly. Moreover, the number of carbides in the microstructure decreased, and their morphology coarsened. Furthermore, the height of the Snoek peak decreased slowly and was accompanied by the gradual disappearance of 2 of the internal friction peaks, P1 and P2.